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Evolution
The World of Darwin
Defensive Adaptations
Animal Defensive Adaptations Hurting your enemy is a good defense; therefore, we should not be surprised by the number of adaptations enabling the owner to do just that.
Stings and Poisons
Many animals, from bumble bees to adders, contain chemicals that are harmful and/or dangerous to others. These chemicals are synthesized and stored predominately within special glands, and they are not allowed to damage the host organism.

When danger threatens, however, these poisons can be forcefully ejected as a sting or a bite, as a spray, or occasionally as an ooze. Their effect is to harm the predator immediately or to act as a distasteful poison in the predator's digestive system if the host is eaten.

Either way, the predator learns to avoid contact with other similar potential victims in the future, and the presence of the gene(s) coding for the sting or poison has thus increased the owner's fitness.

Warning Signals
Smelly, stinging, or bad tasting organisms usually have some means of warning potential predators to leave them alone. Often these adaptations, known as aposematic appearance, take the form of bold color patterns that stand out dramatically against the background.

In South America, for example, lives a bright red-orange frog with large black eyes and dark green-black legs. It is a very obvious animal, yet predators have learned to avoid it carefully because they also know it contains a highly poisonous material.

Possessing genes for highly colored skin increased the frog's chances of survival and enhances its fitness by warding off danger.

Mimics
Some non-dangerous animals, who would make a good meal for a predator nevertheless display body colors and appear to have every aposematic sign that warns of danger.

Flitting across English meadows every summer are two almost identical butterflies. One, the monarch butterfly, contains obnoxious chemicals that make predatory birds feel very sick, if the butterfly is eaten. Birds quickly learn to associate the orange and black wings of this butterfly with feeling very ill, and carefully avoid eating this type of butterfly in the future.

This is a good example of aposematic appearance warning of danger.

A second butterfly, the viceroy, contains none of these chemicals and is good to eat; yet, it too has virtually the same orange and black wings. Consequently, the birds who have learned to avoid the monarch also do not eat the viceroy, mistaking it for one of the inedible monarchs.

In this case, the viceroy is benefiting from its Batesian mimicry of another truly distasteful type of individual. The genes coding for the mimic coloration increase the fitness of the viceroy butterfly by making it appear to be what it is not.

Blending into the Background
Chameleons, flounders, octopuses, and frogs are among a large number of creatures that can change their outward coloration until they blend in so well with their background that they are almost undetectable.

These animals have special pigment cells that can change color and thus protect the animal in a variety of different habitats. Other animals who cannot change their color are adapted with permanent coloration and/or body shape in order to look exactly like something else, preferably something non-edible.

The moth Phalera bucephala looks like a broken twig when it is at rest on a branch; some types of mantis look like leaves; the American bittern (a bird), when posed with its head held high, looks like the reeds and tall grasses in which it waits.

These adaptations for cryptic appearance allow organisms to blend into the background and become harder to detect, making them less likely to be seen or eaten. Once again, a gene or genes has coded for a product or products that has increased an individual's chances of survival and thus increased its fitness.


BIOdotEDU
© 2001, Professor John Blamire